Loud-speaker



Deco 16 193% L. DE FOREST ET AL J 7 LOUD SPEAKER Filed Dec. 1, L926 Jfiz yam Lee .06 firms f Richard f/a/ffl 'iy 4 resultant of the individual "Patented Dec. 16, 1930 UNITED STATES PATENT OFFICE LEE DE FOREST, 0!? NEW YORK, N. Y., AND RICHARD HALPENNY, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNORS, BY MESNE ASSIGNMENTS, TO GENERAL TALK- ING PICTURES CORPORATION, A CORPORATION OF DELAWARE LOUD-SPEAKER Application filed December provision "of a novel combination of elements to form a sound reproducing device, particularly adapted for use in large auditoriums,

as for instance, in connection with the talking motion icture art.

Another 0 ject of this invention is the provision of a sound producing device'comprising the combination of a loud speaker horn and a loud speaker cone in a new and novel relation.

A further object of this invention is the provision of a horn of the 10' arithmic type anda sound reproducing dBVlCG of the cone t pe.

A still further object of this invention is the combination of horn and cone vibrating means in such a manner that the sound produced by each is combined and directed from the opening of the horn.

A further object of this invention is the rovision of a cone loud speaking unit withm the bell of a horn re roducin device to produce a series of soun waves w ich is the oups produced by the horn and cone spea ers. 1

A still further object of this invention is the provision of a baflle plate in the mouth of a large horn speaker in back of which is mounts a cone speaker in alignmentwith an aperture in the baflieplate.

These and many other objects are sou ht by the combination of elements disclose as embodyingthe principles of our invention.

Our inventionresides substantially in the combination, construction, arrangement and relative location of parts as will be clearly disclosed in the following s ecification when taken in connection with tlie drawings.

" Referring to the drawin s in which the same reference numerals wi be used when ossible throughout the several views to incate the same or similarparts,

Figure 1 is a side elevational view of one form of our invention showing the large end of the horn in cross-section Fi 2 is a similar view to Fig. 1 of a modi ed arrangement showing a cone 1, 1926. Serial No. 151,857.

speaker within the bell of the horn speaker s owing the bell portion in cross-section taken on line 22 of Fig. 3;

Fig. 3 is an enlarged view of the bell end of'the construction of Fig. 2 showing a front view thereof;

Fig. 4 is a side view partly in cross-section of the electro-magnetic motive means for the cone speaker.

In the co-pending application, Serial No. 134,781, filed September 11, 1926, by the present Lee de Forest is disclosed an improved loud speaker horn particularly of the logarithmic type adapted for use in motion picture theatres in conjunction with motion picture screens for the production of talking motion pictures. In this application is disclosed. a horn of the logarithmic expansion type especially designed for placement hehind the motion picture screen with its large aperture projecting above or at the side of the screen. A similar arrangement is shown in the present application withrespect to the special relation of the horn with respect to the screen in combination with a cone type of sound reproducing device.

We have found as disclosed in the present application that sound reproduction from such a type of large horn can be materially improved if we combine a loud speaker unit of the cone type with said horn.

Referring to the drawings in Fig. 1 the motion picture screen of any suitable type and construction is shown at 1 and mounted in back thereof and with its major axis extending vertically is a large soundreproducing device of the horn type having at its smaller end, electro-ma'gnetio means of any suitable construction for converting electric current variations into sound waves. The particular ty e of horn disclosed herein, while it may e and is, in its best form of logarithmic type, may however, be of any suitable construction and we only desire to have that form disclosed in the drawings taken in an illustrative sense. The horn is provided at its other extremity with a large ell having a large opening 4 rojecting above the screen or to one side t ereof, or even in back of the screen if found desirable.

An aperture of any suitable configuration,

such as a circle, is provided in'the wall of the bell portion and has mounted in alignment therewith a .cone speaker unit. While we have shown the cone speaker mounted directly on the bell, it is, of course, evident that it may be mounted adjacent thereto but out of shown at 11 opening directly toward the aperture in the bell. WVhile we will describein some detail below, a suitable form of electromagnetic means for vibrating the cone, we do not desire to be limited to this construction since it is at once evident to any one skilled in the art that there are other known forms of cone speakers.

In Fig. 2.as before, there is shown a screen at 1, a large horn at 2, having the electromagnetic sound producing device 3 at its smaller end. In this construction and also shown in Fig.3 there is provided in the opening 4 of the bell, a baffie plate 12 having an aperture 13 at the center in the form of a circle. The bafiie plate 12 forms the front wall of a. casing 14 mounted in back thereof within which is mounted the cone speaker having as above described the casmg 6, terminals 9 and 10 and a cone 11 presenting its free edges towards the aperture; We wish it to be distinctly understood in connection with this form of construction that the casing 14 may be omitted and the cone s eaker mounted within the bell and in bac of the bafiie plate 12 and thereon if desirable.

Referring to Fig. 4, there is shown an electro-magnetic -means for vibrating the cone. An iron cup or casing 15 encloses a field winding 18 having the current terminals 19. Mounted on the cone 22, which has the flexible flange 23, is a moving coil 20 having the'current terminals 21. This coil freely encircles the core 17 and is disposed in the air gap 16 formed by casing 15. When the field 18 is constantly energized, and the varying current representing the sounds to be reproduced pass through the winding 20, the re sulting forces between the fields of these two windings will set the cone 22 in vibration by and in accordance with the varying current-s passing through coil 20.

Wit 1 respect to the baflie plate shown in Figs. 2 and 3, it may be noted that this can be constructed of any suitable material, preferably however, wood. We also desire to point out that the relative proportions of the cone, the baffle plate and the large horn and its bell, may be varied to suit any particular set of acoustic conditions. We have found that the efficiency of a cone type of loud speaker particularly when the cone is of relatively small diameter is greatly increased if said cone is located in the center of the bafiie board, the dimensions of which are such as to proudce sound waves in the lower band of wave lengths of the sound which it is desired to produce with fidelity.

It will be noted that by the particular arrangements disclosed by us, that the sound from the horn and cone will be admitted directly into the surrounding atmosphere and mingled together as though it were coming from a common source. This is particularly true of the arrangement in Figs. 2 and 3. In the arrangement in Fig. 1 the sound from the cone emerges from the aperture of the large horn and mingles with the sound from the large horn itself to produce in effect a composite wave train from a-single source.

It is obvious that such combinations as here shown of a cone and large horn can be obtained in a variety of ways, for example, the large horn does not necessarily have to have the right angle bend at its orifice but can be straight throughout and the ,baflle board with the cone loud speaker arranged two distinct types of loud speakers gives us a distinct advantage in reproduction of sound. By this we mean that the quality of the sound reproduction of such a combination is much better than that from a large horn with a unit at its smaller end having a small diaphragm or from a loud speaker of the cone type, whether it has a cone of small or large diameter. For example, the cone type of speaker, such as illustrated here, wherein the cone is of the order of 6" in diameter is decidedly deficient in the middle tone register. Such a cone will reproduce the lower frequencies down to 150 per second and the higher frequencies from 1,000 or 800 up. However, in the middle range of sound frequencies, it is notably ineflicient. On the other hand, the smaller diaphragm type of loud speakeras shown at 3, combined with the logarithmic horn with aperture is somewhat deficient in the higher frequencies but is-ricli in the middle register frequencies. We have ascertained these peculiarities of these two types of reproducers and have further found that the combination with a horn and cone gives to the resultantsound from the latter alone, an added richness and brilliancy which is very notable.

We have tried various methods of combining these two types of loud speakers and have found that the ones here illustrated, whereby the sounds from the cone and from the horn actually emerge from the same aperture, are far more satisfactory than where the cone loud speaker with or without a bafile board is merelylocated near the large aperture of the cone. At the same time the arrangements shown in the drawings permit the use 'of the logarithmic horn of great flatness which, for reasons already explained in the co-pending application mentioned above, adapts this horn to be attached to the rear of a motion picture screen in such a way as to permit said screen to be raised and lowered among the flies of the theatres without seriously interfering with the battens carrying scenery, drops and the like.

We are, of course, well aware that many changes in the details of construction and even in the relative arrangement of partswill readily suggest themselves to those skilled in the art without departing from the principles of our invention and we do not therefore desire to be limited to the particular constructions disclosed for purposes of illustration,

but rather to our idea 0 the invention as we have defined it in the appended claims.

What we seek to secure Toy United States Letters Patent is:

1. In a loud speaker, the combination with a logarithmic horn and a cone mounted thereon of separate means for vibrating said horn and cone.

2. In aloud speaker construction, the combination with a logarithmic horn having an aperture in the wall thereof of a cone in alignment with said aperture supported on said horn.

3. In a loud speaker construction, the combination with a horn of a cone mounted on said horn so that the sounds from said'cone issue from said horn and separate means for vibrating said cone and horn.

4. In a sound producing construction, the combination with a logarithmic hornhaving a large bell of a vibratilecone mounted within said bell and separate means of difi'erent sound characteristics for actuating said horn and cone.-

5. In a sound roducing device, the combination with a orn having a hell and a bafile plate in said bell of a vibratile cone mounted on back of said plate.

6. In a sound producing device, the combination with a horn having a bell and a bafile plate in said bell of a vibratile cone mounted on back of said plate and means for I vibrating said horn and cone.

7. In a sound producing device, the combination with a horn having a bell and a bathe plate in said bell, having an aperture of a cone mounted on back of said plate and in line with said aperture.

8. In a sound producing device, the combination with a horn having a large aperture bell and a baflie plate in said opening, said plate being apertured, of an enclosing casing of which said plate forms one wall and a cone speaker in said casing mounted in'alignment with said aperture. I

9. In a sound producing construction, the combination with a horn having a bafile plate at its mouth, of a cone speaker mounted on said plate.

10. In a sound producing construction, the.

bination with a horn loud speaker having a large belland an apertured baflle late in the mouth of said horn of a cone s ea er mounted in back of said plate and wlthin said bell and in alignment with the aperture.

In testimony whereof we have hereunto set our hands on this l8thday of November A. D, 1926.

' LEE on FOREST. Y

RICHARD; HALPENNY. 

